Hydraulic vibration damping system for machines provided with tools

ABSTRACT

A hydraulic system for machines provided with tools, particularly for wheel loaders, fork lifts or the like, including comprising at least one hydraulic accumulator, distributing valves, manometric switches and at least one nozzle for variably adapting the load pressure of the hydraulic accumulator to the load pressure of the lifting cylinder, wherein the load-damping system formed by the hydraulic accumulator is connected to the hydraulic lines responsible for lifting and lowering and extending between the hydraulic cylinder(s) and a control valve.

BACKGROUND OF THE INVENTION

The invention relates to a hydraulic system for machines provided withtools, particularly for wheel loaders, fork lifts or the like, having aload-damping system comprising at least one hydraulic accumulatorconnected to the hydraulic lines responsible for lifting and loweringthe tool and that extend between the lifting cylinder and a controlvalve.

Construction machines having pneumatic tires must often travel a longdistance when they are to be used at a construction site. They can bedriven between construction sites and to their locations of use, becausethey fulfill the conditions of admission for participation in publictraffic, even with trailers from time to time.

The driving speeds that can be attained during use contributesignificantly to the transport capability and thus the economical aspectof the machine. However, even for tools that must be transportedfrequently between construction sites, or must use lengthy routes toreach these sites, the time required to do this is a significant factorin the cost calculation of the contractor.

The driving speed of this type of machine is not limited by the enginecapability--with the exception of driving on steep gradients--but by thevibrations the vehicle experiences due to unevenness of the ground. Thedriver is thus obligated to select a speed considerably below the speedthat could be attained. The primary cause of the "bumping" of themachine is the lack of a spring system. Up to now, spring systems haveonly been constructed in construction machines for special purposes, forexample in military applications with the requirement of speeds up toover 60 km/h. The reasons these types of construction machines are builtwithout spring systems are, on the one hand, that a spring system,because of its yielding under lifting and tensile forces, would bedisadvantageous during loading. On the other hand, installing a springsystem represents a relatively high construction expenditure that wouldby nature have to result in considerable additional costs.

From DE-C 3,909,205, a hydraulic system is known for constructionmachines, particularly wheel loaders, tractors and the like, thatinclude a tool, particularly a loading shovel, that is operated by ahydraulic cylinder, wherein a main line is provided for operating thehydraulic cylinder that leads from a pressure source to the hydrauliccylinders via a control valve, from which line a connecting line thatleads to at least one hydraulic accumulator branches off, and in which aswitchable check valve is disposed. A feed line is provided that bridgesthe check valve and connects the main line to the hydraulic accumulator,and a pressure-reducing valve is disposed in the feed line. Thepressure-reducing valve is set to the carrying pressure of the hydrauliccylinder, and is preferably configured as a pressure-limiting valve oras a pressure cut-off valve. The switchable check valve is configured asa magnet valve that is controlled as a function of the driving speed orthe tilting angle of the tool, wherein during driving speed-dependentcontrol of the magnet valve, the switching point is set such that itcannot be exceeded until second gear is reached.

Because only one predeterminable carrying pressure (e.g. 120 bar) can beset in the use of pressure-reducing valves, which cannot be viewed asbeing a realistic value in every working state, the load-damping systemused here is viewed as inadequate for all operating states of themachine. Moreover, the gear- or driving speed-dependent switching of thepressure-reducing valve likewise cannot optimally manage the pitchingvibrations established in the operating state.

SUMMARY OF THE INVENTION

The goal of the subject of the invention is to provide a damping systemfor the tool or the lifting device cooperating therewith such thatpitching vibrations of the machine, particularly those occurring withunfavorable road surfaces, can be reduced.

This goal is achieved in accordance with the invention in that at leastone nozzle connected to a plurality of distributing valves is providedbetween the load-damping system and the lifting cylinder for variablyadapting the load pressure of the hydraulic accumulator to therespective load pressure of the lifting cylinder, wherein the valves canbe operated via manometric switches, and the load-damping system can beactivated or deactivated as a function of predeterminable operatingstates.

The hydraulic system of the invention is particularly suited forconveying and transport trips with an empty or loaded tool.

If the driver operates the pilot control actuator, the distributingvalves are shifted into the neutral position by means of the manometricswitches cooperating with the pilot control actuator, and theload-damping system is disconnected. The hydraulic pressure in thehydraulic accumulator is adapted via the nozzle to correspond to theload pressure in the lifting cylinder. If the driver again puts thepilot control actuator into the neutral position, the load-dampingsystem is automatically activated. After the load pressure has nearlybeen adapted via the nozzle in the hydraulic accumulator, no notablesinking of the tool takes place during automatic deactivation. However,to guard against unacceptable spring deflections of the liftingcylinder(s) via the hydraulic accumulator, the load-damping system isautomatically deactivated via an inductive switch at a specific liftingheight.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject of the invention is described in detail by way of anembodiment. Shown are in:

FIG. 1--representation of a wheel loader; and

FIG. 2--hydraulic circuit diagram for the wheel loader of FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

As a fundamental representation, FIG. 1 shows a wheel loader 1 that cantravel on pneumatic tires 2. The wheel loader 1 includes, among otherfeatures, a chassis 3 that has a driver's cab 4, and a bucket 5 seatedto pivot on a mounting assembly 6, the mounting assembly 6 beingconnected to a plurality of hydraulic cylinders 7, 8 provided for thepurpose of lifting and tilting the bucket 5.

FIG. 2 shows the hydraulic circuit diagram 9 (load-damping system) forthe wheel loader 1 shown in FIG. 1, wherein it is carefully pointed outthat this circuit diagram can be applied in the same manner to othertools, for example a fork lift. In accordance with hydraulic circuitdiagram 9, the load-damping system is connected to the hydraulic lines10, 11 responsible for lifting and lowering, respectively, and thatextend between the lifting cylinders 12, 13 and the control valve 14.The hydraulic line 10 responsible for lifting is connected via a2--2-way valve 15--blocked in the neutral position, free passage in theshift position--to one or a plurality of hydraulic accumulators 16, 17,18, 19. The hydraulic accumulators 16-19 have a vehicle-specific gasbias. A nozzle 21 is located on the lifting side 10 in the bypass 20between the hydraulic accumulators 16-19 and lifting cylinders 12, 13.The hydraulic line 11 responsible for lowering is connected via afurther 2--2-way valve 22--blocked in the neutral position, free passagein the shift position--to the return conduit 23. Manometric switches 29,30, 31, 32 are located in the pilot control lines 24, 25, 26, 27(lifting, lowering, upward tilting, downward tilting), between the pilotcontrol actuator 28 and the control valve 14. On the front frame of thewheel loader 1, which has no further reference numerals, an inductiveswitch 34 is provided at a predetermined height.

A main switch 35 is disposed in the driver's cab 4 of the wheel loader 1for activating and deactivating the load-damping system. When theload-damping system is activated via the main switch, and the pilotcontrol actuator 28 is in the neutral position, the 2--2-way valves 15,22 in the lifting line 10 and the lowering line 11 switch to freepassage. The lifting side 10, that is, lifting cylinders 12, 13, arethus connected to the hydraulic accumulators 16-19. The hydraulic line11 responsible for lowering that is, lifting cylinders 12, 13, areconsequently connected to the return conduit 23. Pitching movements ofthe wheel loader 1 caused by unevenness in the road are hence variablydamped and reduced, e.g. as a function of the respective operatingstate, permitting high driving speeds.

If the driver operates the pilot control actuator 28, the 2--2-wayvalves 15, 22 are switched into the neutral position by means of themanometric switches 29-32, and the load-damping system is deactivated.The hydraulic pressure in the hydraulic accumulators 16-19 is adaptedvia the nozzle 21 to correspond to the load pressure in the liftingcylinders 12, 13. If the driver again puts the pilot control actuator 28into the neutral position, the load-damping system is automaticallydeactivated. After the load pressure in the hydraulic accumulators 16-19has been variably adapted to the respective operating state via thenozzle 21, no notable sinking of the bucket 5 or the mounting assembly 6results.

As a guard against unacceptable spring deflections of the liftingcylinders 12, 13 via the hydraulic accumulators 16-19, the load-dampingsystem is automatically deactivated at a predetermined lifting heightvia the inductive switch 34 on the frame of the wheel loader 1. Forspecific applications, it can be necessary in the operating state of thewheel loader 1 to deactivate the nozzle 21, for example by means of amagnet valve 33.

The function of the hydraulic system of the invention is intended to beclarified by way of a practical example.

During empty runs (empty bucket), the cylinders 12, 13 are under apressure of, for example, 30 bar, and the hydraulic accumulators 16-19are under their own prestress of 18 bar. Because of these pressures, thehighest driving speeds can be achieved during empty travel, whereinvibrations, particularly pitching vibrations, can be suppressed to thegreatest extent.

During loading of the bucket 5, the valves 15 and 22 are switched toneutral via the manometric switches 29-32, and the valve 33 is switchedto passage. The hydraulic accumulators 16-19 are brought to therespective operating pressure via the pressure generated by the pump,not shown, and the nozzle 21. This can result in a pressure ofapproximately 200 bar when the pressure in the hydraulic cylinders 12,13 is 200 bar.

On the wall, a cylinder carrying pressure of 180 bar would beestablished, for example via the magnet valve 33, in the region of thehydraulic cylinders 12, 13, whereas the accumulator pressure wouldapproach this magnet value via the valve 33 and the nozzle 21 in orderto bring about a balance in this manner. As soon as the driver operatesthe pilot control actuator 28, the valves 15 and 22 are switched openvia the manometric switches 29-32, so that the hydraulic accumulators16-19 are connected to the cylinders 12, 13. As already addressed, at apredetermined lifting frame height the inductive switch 34 is operated,and the load-damping system is deactivated.

we claim:
 1. The hydraulic system for wheel loaders provided with ashovel, comprising:at least one lifting cylinder; a control valve; aplurality of hydraulic lines each connected to and extending betweensaid at least one lifting cylinder and said control valve for liftingand lowering the shovel; a load-dumping system comprising at least onehydraulic accumulator connected to said hydraulic lines; a plurality ofdistribution valves; at least one nozzle in connection with saidplurality of distribution valves and located between said at least onehydraulic actuator and said at least one lifting cylinder for variablyadapting a load pressure of said at least one hydraulic accumulator to arespective load pressure of said at least one lifting cylinder; a pilotcontrol actuator; a plurality of pilot control lines connecting saidpilot control actuator and said control valve; and a plurality ofmanometric switches each located within a respective pilot control linebetween said pilot control actuator and said control valve for operatingsaid distribution valves; whereby said load-damping system is activatedand deactivated as a function of a predetermined operating state.
 2. Thehydraulic system as defined in claim 1, wherein said distribution valvesare 2--2-way valves.
 3. The hydraulic system as defined in claim 1,further comprising a bypass line located between said load-dampingsystem and a lifting side of said at least one hydraulic cylinder, saidnozzle being located in said bypass line.
 4. The hydraulic system asdefined in claim 1, wherein the wheel loader includes a front frame;further comprising at least one switch located at a predetermined heighton the front frame.
 5. The hydraulic system as defined in claim 4,wherein said switch comprises an inductive switch.
 6. The hydraulicsystem as defined in claim 1, wherein the wheel loader includes adriver's cab; further comprising a main switch located in the driver'scab for activating said load-damping system.
 7. The hydraulic system asdefined in claim 1, further comprising an additional valve having aclosed position for deactivating said nozzle.
 8. The hydraulic system asdefined in claim 7, wherein said additional valve comprises a magnetvalve.